This invention relates to turbo machinery rotor construction and, more particularly, to structure for axially retaining the rotor blades on the rotor disk of a turbo machine.
Turbo machinery such as high performance gas turbine engines have a compressor and turbine that each includes one or more annular banks or rows of axially spaced fixed stator vanes that are positioned between rows of rotatable rotor blades. Each rotor blade is formed with a rotor tip, an airfoil and a dovetail-shaped base or root that mounts within a mating, generally axial slot formed between adjacent dovetail posts on the web of the rotor disk.
In order to prevent axial movement of the rotor blades, i.e., along the longitudinal axis of the rotor disk and engine, one or more blade retainers are mounted adjacent the axial slots in the rotor disk. Conventional retention systems, however, have inadequate retention capabilities for gas turbines with large axial aerodynamic loads on the blades caused by, for example, compressor stalls, blade rubs, ingestion of objects, and the like.
In an exemplary embodiment of the invention, a blade retention system is provided for a rotating machine having a hub with a plurality of shaped, generally axially extending openings at circumferentially spaced positions about the hub. A plurality of blades having complementary-shaped base portions are received in the openings, and each of the blades is provided with a blade retention slot therein. A circumferential hub slot is formed about a circumference of the hub, wherein the blade retention slots are substantially aligned with the circumferential hub slot when the blades are received in the openings. At least one ring segment is secured in the blade retention slots and the circumferential hub slot. The circumferential hub slot is preferably substantially U-shaped such that an open end of the circumferential hub slot faces a center of the hub, and the blade retention slots are similarly substantially U-shaped such that open ends thereof face the center of the hub. The ring segments preferably extend between 20xc2x0 and 360xc2x0 and preferably 24xc2x0 in one embodiment and 180xc2x0 in another embodiment.
A key may be provided for securing the ring segment in the blade retention slots and the circumferential hub slot. The key includes a hook portion at one end of the key engageable with the ring segment and a threaded portion at an opposite end of the key. In this context, the blade retention system further includes a nut that is cooperatively engageable with the threaded portion of the key. The key is preferably disposed in a hole in the hub that includes a key receiving portion of a first diameter that receives the key and a nut receiving portion of a second diameter, larger than the first diameter to thereby define a shoulder, that receives the nut. The nut is structurally supported by the shoulder to pull the key into locking engagement with the ring segment. An inside diameter of the nut receiving portion may be threaded, and the blade retention system may further include a cap threaded into engagement with the hole in the hub. In an alternative arrangement, the key is disposed in a hole in at least one of the complementary-shaped base portions of the blades.
In another exemplary embodiment of the invention, a blade retention system is provided for a rotating machine including a turbo machinery blade with a dovetail portion shaped to fit into a complementary-shaped opening in a hub for rotation about a hub axis. The blade retention system includes a securing slot defined by (1) a blade retention slot in the turbo machinery blade and (2) a circumferential hub slot formed about a circumference of the hub and substantially aligned with the blade retention slot when the dovetail portion is fit into the complementary-shaped opening in the hub. The blade retention system also includes at least one ring segment engageable with the securing slot to thereby retain the blade from axial displacement.
In yet another exemplary embodiment of the invention, a method of retaining blades in a rotating machine includes the steps of (a) machining a blade slot in each of the plurality of blades, (b) machining a circumferential hub slot about a circumference of the hub such that the blade retention slots are substantially aligned with the circumferential hub slot when the blades are received in the openings, (c) positioning the blades in the openings, and (d) securing at least one ring segment in the blade retention slots and the circumferential hub slot. Step (d) may be practiced by inserting at least one key having a key opening adjacent the blade retention slots and the circumferential hub slot, fitting the at least one ring segment into the key opening, and urging the key toward the blade retention slots and the circumferential hub slot. Step (d) may further be practiced by forming a hole in one of the hub or base portions of the blades, and inserting the key into the hole prior to fitting the ring segment into the key opening. Step (d) may be still further practiced by forming threads at an inside diameter of the hole and threading the cap to the hole.